This invention relates to a one-part moisture-curable urethane composition, a method of providing a protective coating by application of the composition to a substrate, and to substrate such as wood coated therewith.
Coatings containing polyurethane are very popular because they provide a clear coating on wood which has flexiblity, thoughness, abrasion resistance, and chemical resistance. The polyurethane coating may be either a two-component or a one-component system. The two-component systems are genrally inconvenient to use because they have a short pot life and are difficult to apply. The use of two-component systems as a wood finish is thus generally limited to professionals.
The one-component, moisture-cureable polyurethane systems are well known as clear wood finishes. One type, the isocyanate modified drying oil or urethane oil, depends for its final curing upon the oxidative polymerization of double bonds of the drying oil fatty acid portion. Another type, the so-called blocked isocyanate coating system, involves the heat curing of an end-capped isocyanate which is blocked by phenol or ketoxime that is curable with a polyol via thermal regeneration of the isocyanate.
U.S. Pat. No. 4,222,909, issued to D. W. Brixius et al, discloses a moisture curable coating composition comprising low molecular weigh isocyanate functional acrylic polymer having a terminal thioalkyl group based on the copolymerized isocyanatoalkyl methacrylate. U.S. Pat. No. 4,217,436, issued to Richter et al, discloses the use of a novel bis cyclic urea blend with polymeric polyols to form one-component room temperature stable curable composition. The bis cyclic urea is easily converted to aliphatic diisocyanate simply by heating. U.S. Pat. No. 4,565,857, issued to Grant, discloses a protective coating system comprising a polymerizable ethylenically unsaturated compound having an isocyanate group reacted with the hydroxyl groups of the celluose ester. This thermoplastic polymer can be coated on a wood surface by conventional methods and, following a final cure, thermoset by exposure to ultra violet light. U.S. Pat. No. 4,600,790, issued to Eck et al discloses a moisture curable composition containing SiC-bonded biuret groups, which is prepared by reacting amino functional silane with mono or diisocyanates, that serves as an additive to lacquers. U.S. Pat. No. 4,289,869, issued to Zengel et al, describes a moisture curable mixture containing polysocyanate and polyepoxide with an N,N'-substituted imidazolidine or hexahydropyrimidine derivative as a moisture activated hardener. U.S. Pat. No. 4,625,012, issued to Risk et al, discloses the preparation of a moisture curable polyurethane polymer containing terminal socyanate and alkoxysilane by a two-step reaction route, to provide a sealing material for non-porous surfaces such as glass and ceramic. U.S. Pat. No. 4,539,345, issued to Hansen, teaches one-part moisture-curable polyurethane adhesive, coating, sealant, or casting compositions based on a blend of isocyanate-functional prepolymer, terpene-phenolic resin, and a silane compound.
The polyurethane coating compositions disclosed in the cited prior art have problems or disadvantages. For example, the cellulose-type urethane coatings lack the ability to provide heat and stain resistance, oil-type urethane systems require the use of heat and UV radiation for curing, polymerizable isocyanate-silane polymers have a relatively short pot life due to high molecular weight, and some coatings are complicated to use and/or are relatively expensive to prepare because they use sophisticated materials. Many of these disadvantages can be overcome by the present invention.